The development in inflammatory exudates of antigen activated T-cells will be correlated with their profile of surface membrane markers, capacity to release macrophage migration inhibitory factor (MIF) and ability to cooperate with B-cells in the antibody response to soluble antigens of Listeria monocytogenes. Velocity sedimentation, vinblastine and affinity chromatography will be used to determine the size, turnover and presence on protective T-cells of receptors for rat imunoglobulin or immune complexes. Arrival of labelled T-cells in induced peritoneal exidates will be correlated with the ability of exudate cells to release MIF and operate as helper cells in the antibody response to Listeria antigens. BIBLIOGRAPHIC REFERENCES: McGregor, D.D. and P.S. Logie. The mediator of cellular immunity. VIII. Effect of mitomycin C on specifically sensitized lymphocytes. Cell. Immunol., 15, 69 1975. Kostiala, A.A.I. and D.D. McGregor. The mediator of cellular immunity. IX. The relationship between cellular hypersensitivity and cellular resistance in rats infected with Listeria monocytogenes. J. Exp. Med., 141, 1249, 1975.